There are many types of electrical circuits that employ filters. Circuits designed for transmitting and receiving communication signals, for example, typically include various types of filters, including low-pass filters, high-pass filters, and band-pass filters. Such communication circuits may be used in a wide variety of devices and applications, including telephones, televisions, wireless computing devices, audio devices, personal data assistants (PDAs), and any other suitable systems that communicate signals. Of course, in addition to communications circuits, many other types of electrical circuits may include filters.
It is known that the operational performance of a filter may vary depending upon several factors. For a conventional low-pass filter composed of a combination of elements (e.g. operational amplifiers, capacitors, resistors, etc.), a desired cutoff frequency of the filter may vary considerably during operation, depending upon the processing loads and environmental variations (e.g. temperature variations) experienced by the filter.
A conventional approach to handling such operational variation is to design the surrounding components of the electrical circuit in such a way that they tolerate a shift in the filter's performance. Another approach is to use a separate reference circuit to measure the filter's performance, and then selectively switch resistive or capacitive elements on or off to tune the filter's operational performance as needed. Unfortunately, such conventional approaches are not ideal and may ignore certain side effects that lead to other operational inaccuracies. Novel techniques that mitigate a filter's operational variation while also improving upon undesirable aspects of the prior art would have considerable utility.